Thrust bearing assembly for a rotor of an electric motor, in particular for electric pumps
The thrust bearing assembly separates radial and axial thrust support functions, reducing wear and costs by using a thrust bearing bushing and sleeve configuration, enabling a shorter, less expensive bushing design for electric motors.
Patent Information
- Authority / Receiving Office
- WO · WO
- Patent Type
- Applications
- Current Assignee / Owner
- MECCANOTECNICA UMBRA SPA
- Filing Date
- 2025-12-10
- Publication Date
- 2026-06-18
AI Technical Summary
Existing thrust bearings in electric motors, particularly in pumps, face issues with wear due to axial thrusts, leading to motor blockage and high costs due to the use of expensive materials for bushings that need to support both radial and axial thrusts.
A thrust bearing assembly is introduced that separates the functions of radial and axial thrust support, using a thrust bearing bushing and a box fixed to the rotor, with a sleeve fixed to the stator, allowing the bushing to be shorter and made of less expensive materials, while the thrust bearing bushing supports only axial thrusts.
The solution reduces wear, minimizes the axial extension of the bushing, and lowers costs by allowing the use of less expensive materials, ensuring a reliable and long-lasting operation.
Smart Images
Figure IB2025062652_18062026_PF_FP_ABST
Abstract
Description
[0001] THRUST BEARING ASSEMBLY FOR A ROTOR OF AN ELECTRIC MOTOR, IN PARTICULAR FOR ELECTRIC PUMPS
[0002] DESCRIPTION
[0003] The present invention relates to a thrust bearing assembly for a rotor of an electric motor, in particular for electric pumps.
[0004] With reference to Figs. 1 and 2, a generic electric motor (200) comprising a rotor (2) rotatably mounted in a housing (10) of a stator (1 ) is shown.
[0005] In the case where the electric motor (200) is part of a pump (201 ), an impeller (20) of the pump is connected to the rotor (2) so as to rotate and allow a fluid to be delivered or sucked.
[0006] The electric motor (200) comprises a shaft (15) fixedly mounted in the stator (1 ) in such a way to be arranged axially in the housing (10) of the stator. By way of example, the shaft (15) is fixed or keyed in a hole (1 1 ) of a bottom wall (12) of the stator.
[0007] The rotor (2) is rotatably mounted on the shaft (15) by means of a bushing (3). The bushing (3) is fixedly arranged in an axial hole (21 ) of the rotor. The bushing (3) has an axial hole (30) and is rotatably mounted on the shaft (15).
[0008] The bushing (3) has a first end (31 ) facing the bottom wall (12) of the stator and a second end (32) opposite the first end.
[0009] A locking washer (16) is arranged at one end of the shaft (15) so as to be located in a seat (22) of the rotor and abut against the second end (32) of the bushing. A retaining ring (17), such as a Seeger ring, is disposed in a seat (18) at the end of the shaft to lock the locking washer (16).
[0010] During the operation of the electric motor (200), the rotor (2) is subjected to axial thrusts in the directions of the arrows F1 and F2. The axial thrusts are exclusively compensated by the bushing (3). In fact, if the axial thrusts of the rotor are in the direction of the arrow F1 , the first end (31 ) of the bushing abuts against the bottom wall (12) of the stator. If the axial thrusts are in the direction of the arrow F2, the second end (32) of the bushing abuts against the locking washer (16) of the shaft of the stator.
[0011] Generally speaking, in pump applications, the force in the direction of the arrow F1 does not occur because the rotor is mounted in an axial position that is slightly set back with respect to the stator in such a way that the magnetic field always produces a thrust in the direction of the arrow F2, and because during the operation the impeller is subjected to a hydraulic thrust in the direction of the arrow F2. However, there may be situations in which the force in the direction of the arrow F1 is temporarily present.
[0012] Therefore, the bushing (3) has a dual function, acting as radial support to compensate for the radial thrusts during the rotation of the rotor, and as axial support to compensate for the axial thrusts to which the rotor is subjected during the operation of the motor.
[0013] Mainly due to the axial thrusts in the direction of the arrow F2, after a certain period of operation, the bushing (3) tends to wear out, causing the impeller to move forward and touch the volute of the pump, thus blocking the motor.
[0014] For such a reason, the bushing (3) is generally made of a highly performing technical material, such as carbon. As a result, a bushing for an electric motor according to the prior art can be very expensive.
[0015] Furthermore, it must be considered that, in a structure such as that illustrated above, a bushing must have a very long axial length so that its ends (31 , 32) abut against the bottom wall (12) of the stator and the locking washer (16) of the shaft of the stator.
[0016] EP2462351 discloses a liquid pump wherein the rotor of the pump comprises a bushing rotatably mounted on a shaft of the stator. A cover of the stator has a tang that abuts against one end of the bushing. In this way, the bushing can support radial thrusts during a rotation of the rotor as well as axial thrusts during an axial movement of the rotor relative to the stator.
[0017] US6443710B1 discloses a pump wherein the rotor of the pump comprises a bushing rotatably mounted on a shaft of the stator. A cover of the stator has a thrust bearing that abuts against a bearing mounted at one end of the bushing of the rotor. In this way, the bushing can support radial thrusts during a rotation of the rotor as well as axial thrusts during an axial movement of the rotor relative to the stator.
[0018] The purpose of the present invention is to eliminate the drawbacks of the prior art by providing a thrust bearing assembly for a rotor of an electric motor that is suitable for solely and exclusively supporting axial thrust.
[0019] Another purpose is to provide such a thrust bearing assembly that can be applied to a pump motor of known type as a single element, in such a way that the bushing of the pump motor only supports the radial thrusts during the rotation of the rotor and the bushing of the thrust bearing assembly only supports the axial thrusts due to the sliding motion of the rotor relative to the stator.
[0020] Another purpose is to provide such a thrust bearing assembly for a rotor of an electric motor that is reliable and long-lasting over time.
[0021] Another purpose is to provide such a thrust bearing assembly for a rotor of an electric motor that is versatile, inexpensive, and easy to install.
[0022] Another purpose is to provide such a thrust bearing assembly for a rotor of an electric motor that is capable of minimizing the axial extension of the bushing of the motor.
[0023] These purposes are achieved in accordance with the invention with the characteristics of the appended independent claim 1 .
[0024] Advantageous embodiments of the invention appear from the dependent claims.
[0025] Further features of the invention will become clearer from the detailed description below, referring to purely exemplary and therefore non-limiting embodiments, illustrated in the appended drawings, wherein:
[0026] Fig. 1 is an axial sectional view of an electric motor of an electric pump according to the prior art;
[0027] Fig. 2 is an exploded perspective view of the electric motor of Fig. 1 ;
[0028] Fig. 3 is an axial sectional view of an electric motor of an electric pump provided with a thrust bearing assembly according to the invention; Fig. 3A is an enlarged view of a detail of Fig. 3, illustrating the thrust bearing assembly according to the invention;
[0029] Fig. 4 is an exploded perspective view of the electric motor of Fig. 3;
[0030] Fig. 5 is a perspective view illustrating the thrust bearing assembly of Fig. 4;
[0031] Fig. 6 is an axial sectional view of a second embodiment of the thrust bearing assembly according to the invention;
[0032] Fig. 7 is an exploded perspective view of the thrust bearing assembly of Fig. 6;
[0033] Fig. 8 is an axial sectional view of a third embodiment of the thrust bearing assembly according to the invention;
[0034] Fig. 9 is an exploded perspective view of the thrust bearing assembly of Fig. 8;
[0035] Fig. 10 is an axial sectional view of a fourth embodiment of the thrust bearing assembly according to the invention;
[0036] Fig. 1 1 is an exploded perspective view of the thrust bearing assembly of Fig. 10;
[0037] Fig. 12 is an exploded axial sectional view of a variant of the thrust bearing assembly of Fig. 8;
[0038] Fig. 13 is a perspective view of the assembled thrust bearing assembly of Fig. 12; and
[0039] Fig. 14 is a sectional view of the thrust bearing assembly of Fig. 13.
[0040] With reference to Figs. 3, 3A and 4, an electric motor (100) comprising a rotor (2) rotatably mounted in a housing (10) of a stator (1 ) is illustrated.
[0041] In the case where the electric motor (200) is part of a pump (101 ), an impeller (20) of the pump is connected to the rotor (2) in such a way to rotate and allow a fluid to be delivered or sucked.
[0042] The electric motor (100) comprises a shaft (15) fixedly mounted in the stator (1 ) in such a way to be arranged axially in the housing (10) of the stator. By way of example, the shaft (15) is fixed or keyed in a hole (1 1 ) of a bottom wall (12) of the stator. The rotor (2) is rotatably mounted on the shaft (15) by means of a bushing (3). The bushing (3) is fixedly arranged in an axial hole (21 ) of the rotor. The bushing (3) has an axial hole (30) and is rotatably mounted on the shaft (15).
[0043] The bushing (3) has a first end (31 ) facing the bottom wall (12) of the stator and a second end (32) opposite the first end.
[0044] The rotor (2) has a seat (22) with a diameter greater than the diameter of the axial hole (21 ) of the rotor.
[0045] According to the invention, the electric motor (100) comprises a thrust bearing assembly (A) suitable for supporting the axial thrusts of the rotor (2). In this way, the bushing (3) is suitable for supporting only the radial thrusts of the rotor (2).
[0046] The thrust bearing assembly (A) comprises:
[0047] - a box (4) suitable for being fixed to the rotor (2);
[0048] - a thrust bearing bushing (5) arranged and fixed in the box (4), and
[0049] - a first sleeve (6) suitable for being fixed to the shaft (15) of the stator.
[0050] The first sleeve (6) is arranged in the thrust bearing bushing (5) so that the thrust bearing bushing (5) can rotate with respect to the first sleeve (6).
[0051] The box (4) comprises:
[0052] - a cylindrical wall (40) which is arranged in the axial hole (21 ) of the rotor, and
[0053] - a collar (61 ) which is arranged on the seat (22) of the rotor.
[0054] A plurality of fins (42) protrude radially towards the inside from the cylindrical wall (40) of the box.
[0055] The box (4) is made of sheet metal.
[0056] The thrust bearing bushing (5) comprises an axial hole (50) having a polygonal profile, for example a hexagonal profile.
[0057] The thrust bearing bushing (5) comprises a first end (51 ) and a second end (52).
[0058] The first end (51 ) of the thrust bearing bushing is provided with a plurality of radial seats (53) suitable for receiving the fins (42) of the box to stop a relative rotation of the thrust bearing bushing (5) with respect to the box (4). The thrust bearing bushing (5) is made of sintered metal material, hard plastic, silicon carbide, alumina carbide, graphite, or PTFE.
[0059] The first sleeve (6) comprises a cylindrical body and axial retaining means (M1 ). In such a first embodiment, the axial retaining means (M1 ) comprise a collar (61 ) protruding outwardly from the cylindrical body (60) of the first sleeve. The first sleeve (6) has an axial hole (50) wherein the shaft (15) of the stator is forcedly inserted, so as to secure the shaft (15) to the first sleeve (6).
[0060] The cylindrical body (60) of the first sleeve is disposed in the axial hole (50) of the thrust bearing bushing so that the thrust bearing bushing (5) rotates relative to the cylindrical body (60) of the first sleeve. Therefore, the walls of the axial hole (50) of the thrust bearing bushing are tangent to the outer surface of the cylindrical body (60) of the first sleeve.
[0061] The collar (61 ) of the first sleeve is arranged on the second end (52) of the thrust bearing bushing and abuts against the second end (52) of the thrust bearing bushing to compensate for the axial thrusts of the rotor (2) acting on the thrust bearing bushing. The second end (52) of the thrust bearing bushing slides on the collar (61 ) of the first sleeve.
[0062] The first sleeve (6) is made of sheet metal.
[0063] The second end (52) of the thrust bearing bushing may have a concave shape from the outside toward the inside; that is to say, in an axial sectional view, the second end (52) of the thrust bearing bushing is inclined towards a point on the axis of the bushing that is located inside the axial hole (50) of the bushing. In such a case, also the collar (61 ) of the first sleeve is concave.
[0064] The second end (52) of the thrust bearing bushing may have a convex shape from the outside to the inside; that is to say, in an axial sectional view, the second end (52) of the thrust bearing bushing is inclined toward a point on the axis of the bushing that is located outside the axial hole (50) of the thrust bearing bushing. In such a case, also the collar (61 ) of the first sleeve is convex.
[0065] Therefore, the collar (61 ) of the first sleeve and the second end (52) of the thrust bearing bushing (5) have concave / convex sliding surfaces with an inclination relative to a straight line orthogonal to the axis of the shaft (15) comprised in a range between +10° and -10°.
[0066] The second end (52) of the thrust bearing bushing may be flat from the outside to the inside; that is to say, in an axial sectional view, the second end (52) of the thrust bearing bushing is orthogonal to the axis of the bushing. In such a case, also the collar (61 ) of the first sleeve is flat.
[0067] It should be noted that the first end (51 ) of the thrust bearing bushing is located in the axial hole (21 ) of the rotor, in a very distal position from the second end (32) of the bushing (3). Therefore, the thrust bearing bushing (5) does not interfere with the bushing (3). Thus, the bushing (3) only has the function of supporting the radial thrusts of the rotor; conversely, the thrust bearing bushing (5) only has the function of supporting the axial thrusts of the rotor (2), and not the radial thrusts of the rotor.
[0068] Hereafter, elements identical or corresponding to those already described are indicated with the same reference numerals, omitting their detailed description.
[0069] Figs. 6 and 7 illustrate a second embodiment of the thrust bearing assembly (A) suitable for supporting the axial thrusts in two opposite directions.
[0070] In such a case, the thrust bearing assembly (A) also comprises second axial retaining means (M2) fixed to the cylindrical body (60) of the first sleeve under the thrust bearing bushing (5) and suitable for retaining an axial thrust of the thrust bearing bushing (5) to prevent it from slipping out of the body of the first sleeve.
[0071] The second axial retaining means (M2) comprise a second sleeve (7) having an axial hole (72) and a cylindrical body (70) and a collar (71 ) protruding outwardly from the cylindrical body (70) of the second sleeve.
[0072] In such a case, the cylindrical body (70) of the second sleeve is forcedly disposed inside the cylindrical body (60) of the first sleeve; therefore, the shaft (15) of the stator is fixed inside the cylindrical body (70) of the second sleeve.
[0073] The collar (71 ) of the second sleeve abuts against the first end (51 ) of the thrust bearing bushing (5). Therefore the thrust bearing bushing (5) is compressed in sandwich-configuration between the collar (71 ) of the second sleeve and the collar (61 ) of the first sleeve. In any case, the first end (51 ) of the thrust bearing bushing slides against the collar (71 ) of the second sleeve.
[0074] The second sleeve (7) is made of sheet metal.
[0075] Therefore, if the rotor (2) undergoes an axial thrust in the direction of the arrow F1 , the thrust bearing bushing (5) pushes the second sleeve (7) fixed to the shaft of the stator (1 ).
[0076] Conversely, if the rotor (2) undergoes an axial thrust in the direction of the arrow F2, the thrust bearing bushing (5) pushes the first sleeve (6) fixed to the second sleeve (7) that is fixed to the shaft of the stator (1 ).
[0077] The first end (51 ) of the thrust bearing bushing may have a concave shape from the outside towards the inside; that is to say, in an axial sectional view, the first end (51 ) of the thrust bearing bushing is inclined towards a point on the axis of the bushing that is located inside the hole (50) of the bushing. In such a case, also the collar (71 ) of the second sleeve is concave.
[0078] The first end (51 ) of the thrust bearing bushing may have a convex shape from the outside towards the inside; that is to say, in an axial sectional view, the first end (51 ) of the thrust bearing bushing is inclined towards a point on the axis of the bushing that is located outside the hole (50) of the thrust bearing bushing. In such a case, also the collar (71 ) of the second sleeve is convex.
[0079] The first end (51 ) of the thrust bearing bushing may be flat from the outside towards the inside; that is to say, in an axial sectional view, the first end
[0080] (51 ) of the thrust bearing bushing is orthogonal to the axis of the bushing. In such a case, also the collar (71 ) of the second sleeve is flat.
[0081] Figs. 8 and 9 illustrate a third embodiment of the thrust bearing assembly (A) further comprising a first thrust bearing ring (8) disposed on the second end
[0082] (52) of the thrust bearing bushing (5).
[0083] The first thrust bearing ring (8) has a hole (80) wherein the cylindrical body (60) of the first sleeve (6) is arranged.
[0084] The first thrust bearing ring (8) has a first end (81 ) disposed on the second end (52) of the thrust bearing bushing. In this way, the second end (52) of the thrust bearing bushing slides on the first end (81 ) of the first thrust bearing ring (8).
[0085] The first thrust bearing ring (8) has a second end (82) opposite the first end (81 ). A plurality of radial seats (83) are formed in the second end (82) of the first thrust bearing ring (8).
[0086] Instead of comprising a continuous collar, the axial retaining means (M1 ) of the first sleeve (6) comprise a plurality of fins (63) that protrude radially outwards to engage the radial seats (83) of the first thrust bearing ring. In this way, in addition to ensuring an axial retention of the first thrust bearing ring (8), the axial retaining means (M1 ) of the first sleeve (6) also act as anti-rotation means, preventing a relative rotation between the first sleeve (6) and the first thrust bearing ring (8).
[0087] Being fixed to the box (4), which is fixed to the rotor, the thrust bearing bushing (5) rotates together with the rotor (2). Instead, the first thrust bearing ring (8) is integral with the shaft (15). Therefore, the thrust bearing bushing slidingly rotates on the first thrust bearing ring.
[0088] The first thrust bearing ring (8) is made of sintered metal material or plastic.
[0089] Figs. 10 and 11 illustrate a fourth embodiment of the thrust bearing assembly (A), suitable for supporting the axial thrusts in two opposite directions.
[0090] In such a case, in addition to the second sleeve (7), the thrust bearing assembly (A) also comprises a second thrust bearing ring (9) disposed on the first end (51 ) of the thrust bearing bushing.
[0091] The second thrust bearing ring (9) has a hole (90) for the insertion of the cylindrical body (70) of the second sleeve (7).
[0092] The second thrust bearing ring (9) has a first end (91 ) and a second end (92) arranged on the first end (51 ) of the thrust bearing bushing. In this way, the first end (51 ) of the thrust bearing bushing slides on the second end (92) of the second thrust bearing ring (9).
[0093] A plurality of radial seats (93) are formed in the first end (91 ) of the second thrust bearing ring. Instead of comprising a continuous collar, the second axial retaining means (M2) of the second sleeve (7) comprise a plurality of fins (73) that protrude radially outward to engage the radial seats (93) of the second thrust bearing ring. In such a way, the second axial retaining means (M2) of the second sleeve (7) not only ensure an axial retention of the second thrust bearing ring (9), but also act as anti-rotation means, preventing a relative rotation between the second sleeve (7) and the second thrust bearing ring (9).
[0094] Being fixed to the box (4), which is fixed to the rotor, the thrust bearing bushing (5) rotates together with the rotor (2). Conversely, the first thrust bearing ring (8) and the second thrust bearing ring (9) are integral with the shaft (15) of the stator and are therefore fixed. So, the thrust bearing bushing (5) slidingly rotates on the first thrust bearing ring (8) and on the second thrust bearing ring (9).
[0095] The second thrust bearing ring (9) is made of sintered metal material or plastic.
[0096] Therefore, if the rotor (2) undergoes an axial thrust in the direction of the arrow F1 , the thrust bearing bushing (5) pushes the second thrust bearing ring (9) that is held by the second sleeve (7) fixed to the shaft of the stator (1 ).
[0097] Conversely, if the rotor undergoes an axial thrust in the direction of the arrow F2, the thrust bearing bushing (5) pushes the first thrust bearing ring (8) that is held by the first sleeve (6) fixed to the second sleeve (7) fixed to the shaft of the stator.
[0098] With reference to Figs. 12 to 14, in a variant of the second embodiment of the thrust bearing assembly (A), the collar (61 ) of the first sleeve has an annular portion (65) parallel to the cylindrical body (60) of the first sleeve. The annular portion (65) of the collar of the first sleeve has seats (66) suitable for accommodating radial projections (86) protruding from the first thrust bearing ring (8). In this way, the first thrust bearing ring (8) is integral with the first sleeve (6).
[0099] The thrust bearing bushing (5) is integral with the box (4) by interference, i.e., forced pressure coupling. In such a case, the second axial retaining means (M2) comprise a locking ring (300) fixed to the cylindrical body (60) of the first sleeve (6) under the thrust bearing bushing (5) and the box (4). The locking ring (300) prevents the assembly comprising the box (4) and the thrust bearing bushing (5) from axially slipping out of the cylindrical body (60) of the first sleeve, separating from the assembly comprising the first sleeve (6) and the first thrust bearing ring (8).
[0100] The use of the thrust bearing assembly (A) in an electric motor (100) allows the bushing (3) of the electric motor to be released from its function of supporting the axial thrusts.
[0101] In this way, the bushing (3) can be shorter than in the prior art. Otherwise said, the length of the bushing (3) can be halved compared to the length of a bushing according to the prior art that is used to support also the axial thrusts.
[0102] Furthermore, the bushing (3) can be made of a less-performing and more economical material. Otherwise said, instead of being made of carbon, the bushing (3) can be made of sintered metal or even hard plastic.
[0103] Numerous modifications can be made to the present embodiment of the invention, which are within the reach of an expert of the field and fall in any case within the scope of the invention as disclosed by the attached claims.
Claims
CLAIMS1. Thrust bearing assembly (A) for a rotor (2) of an electric motor (200); said thrust bearing assembly (A) comprising:- a box (4) suitable for being attached to the rotor (2),- a thrust bearing bushing (5) disposed and fixed in the box (4); said thrust bearing bushing (5) having a first end (51 ), a second end (52) and an axial hole (50), and- a first sleeve (6) suitable for being fixed to a shaft (15) integral with a stator (1 ) of the electric motor; wherein said first sleeve (6) is disposed into said axial hole (50) of the thrust bearing bushing (5), in such a way to let the thrust bearing bushing (5) rotate with respect to said first sleeve (6); and said first sleeve (6) having axial retaining means (M1 ) suitable for retaining an axial thrust of said thrust bearing bushing (5); wherein the thrust bearing bushing (5) only has the function of supporting the axial thrusts of the rotor (2), and not the radial thrusts of the rotor.
2. The thrust bearing assembly (A) according to claim 1 , wherein; said first sleeve (6) comprises a cylindrical body (60) and an axial hole (62) suitable for receiving a shaft (15) of the stator so that said shaft of the stator is fixed to the first sleeve (6); and said axial retaining means (M1 ) of the first sleeve comprise a collar (61 ) protruding externally from the cylindrical body (60) to abut against said second end (52) of the thrust bearing bushing that slides on said collar (61 ) of the first sleeve.
3. The thrust bearing assembly (A) according to claim 1 or 2, wherein said thrust bearing bushing (5) comprises radial seats (55) machined in said first end (51 ); and said box (4) comprises a cylindrical wall (40) and a plurality of fins (42) radially projecting towards the inside of the cylindrical wall (40) of the box to engage said radial seats (55) of the thrust bearing bushing.
4. The thrust bearing assembly (A) according to any of the preceding claims, wherein said axial hole (50) of the thrust bearing bushing (5) has a polygonal shape.
5. The thrust bearing assembly (A) according to any of the preceding claims, further comprising second axial retaining means (M2) fixed to said body (60) of the first sleeve under said thrust bearing bushing (5) and suitable for retaining an axial thrust of said thrust bearing bushing (5) to prevent it from slipping out of the body of the first sleeve.
6. The thrust bearing assembly (A) according to claim 5, wherein said second axial retaining means (M2) comprise a second sleeve (7) suitable for being fixed to a shaft (15) of the stator; wherein said second sleeve (7) is disposed and fixed in said first sleeve (6).
7. The thrust bearing assembly (A) according to claim 6, wherein said second sleeve (7) comprises a cylindrical body (70) and an axial hole (72) suitable for receiving a shaft (15) of the stator in such a way that said shaft of the stator is fixed to the second sleeve (7); and said second axial retaining means (M2) of the second sleeve comprise a collar (71 ) protruding externally from said cylindrical body (70) to abut against said first end (51 ) of the thrust bearing bushing that slides on said collar (71 ) of the second sleeve.
8. The thrust bearing assembly (A) according to claim 5, wherein said second axial retaining means (M2) comprise a locking ring (300) fixed to the cylindrical body (60) of the first sleeve (6) under the thrust bearing bushing (5).
9. The thrust bearing assembly (A) according to any of the preceding claims, further comprising a first thrust bearing ring (8) fixed to said first sleeve (6) and disposed on said second end (52) of the thrust bearing bushing to let the second end (52) of the thrust bearing bushing slide on said first thrust bearing ring (8).
10. The thrust bearing assembly (A) according to claim 9, wherein said first thrust bearing ring (8) has a first end (81 ) facing said second end (52) of the thrust bearing bushing and a second end (82) wherein a plurality of radialseats (83) are formed; and said axial retaining means (M1 ) of the first sleeve (6) comprise fins (63) projecting radially outwardly to engage said radial seats (83) of the first thrust bearing ring.
11. The thrust bearing assembly (A) according to any of claims 6 to 10, further comprising a second thrust bearing ring (9) fixed to said second sleeve (7) and arranged on said first end (51 ) of the thrust bearing bushing to let the first end (51 ) of the thrust bearing bushing slide on said second thrust bearing ring (9).
12. The thrust bearing assembly (A) according to claim 11 , wherein said second thrust bearing ring (9) has a first end (91 ) and a second end (92) facing said first end (51 ) of the thrust bearing bushing and a plurality of radial seats (93) formed in said first end (91 ) of the second thrust bearing ring; and said second axial retaining means (M2) of the second sleeve (7) comprise fins (73) projecting radially outwardly to engage said radial seats (93) of the second thrust bearing ring.
13. The thrust bearing assembly (A) according to any of claims 2 to 12, wherein the collar (61 ) of the first sleeve and the second end (52) of the thrust bearing bushing (5) have concave / convex sliding surfaces with inclination comprised in a range between +10° and -10° with respect to a straight line orthogonal to the axis of the shaft (15).
14. Electric motor (100) comprising:- a stator (1 ) with a shaft (15) disposed axially in a housing (10) of the stator,- a rotor (2) rotatably mounted in the housing (10) of the stator,- a bushing (3) fixed to the rotor (2) and rotatably mounted on the shaft (15) of the stator, and- a thrust bearing assembly (A) according to any of the preceding claims.
15. Electric pump (101 ) comprising an electric motor (100) according to claim 14, wherein an impeller (20) of the pump is connected to said rotor (2) of the electric motor.